Transglutaminase Effects on Texture and Flow Behaviour of Fermented Milk During Storage Using Concentrated Kombucha Inoculum

This study investigated the effect of a concentrated kombucha inoculum and transglutaminase (TG) on the rheological and textural properties of fermented milk products and compared their average production costs to commercial yoghurt. Semi-skimmed milk was used, to which microbial TG was added at a level of 0.02% w/w. The kombucha inoculum, prepared from black tea, was concentrated to 55.6% total solids. Four samples were produced: two with TG and two without. The TG-containing samples showed significantly higher textural properties, including firmness and consistency, than the non-TG samples. They also exhibited the largest hysteresis loop area and the highest yield stress, indicating a stronger gel structure. The Herschel–Bulkley model successfully described the flow behaviour of all samples and confirmed their shear-thinning, non-Newtonian nature. Principal Component Analysis (PCA) showed that both TG addition and inoculum concentration significantly influenced the product properties. TG improved the rheological and textural properties and increased the stability during storage. However, the production costs for TG-treated samples were higher than those for non-TG-treated samples and commercial yoghurt. Nevertheless, the higher costs could be justified by the perceived additional nutritional benefits for consumers. Overall, the results show that the combination of concentrated kombucha inoculum with transglutaminase can improve the structural and rheological quality of fermented dairy products, which is potentially of commercial importance.